“Caching-In” for SharePoint

Performance

Sean McDonough

Product Manager, SharePoint Products

Idera

Session overview

Caching 101

Understanding each of SharePoint’s

platform caching options

How to leverage and control caching

Warnings and watch-outs

Q&A

Why I care about caching

• Formerly the architect for a Fortune 50’s

publicly facing SharePoint presence

• Highly trafficked environment – ~75,000 page views per hour peak (2009)

– Usually 40 SP-hosted assets per page or more

– Greater than 1000 requests/second into IIS

• Supported with a single farm (4 WFEs)

• Tired of “SharePoint doesn’t scale” claims

Caching 101

Cache: what is it?

Web Part caching

post-cache substitution

Office viewing service cache

virtual memory

disk-based caching

BLOB cache

page-output cache

in-memory cache

object cache

browser cache

edge caching

cacheability headers

buffer fragment caching

CARP

ICP

HTCP

Cache: what is it?

• A temporary storage area where frequently

accessed data can be stored for rapid

access

• Rapid access facilitated in two ways Data is placed on a faster medium

Data is moved closer to point of usage

• Typically used for data that is expensive to

fetch or calculate

Why caching for SharePoint?

Consider a page request from a client Page rendering requires constituent control rendering

w/ merging of file system & DB data

Each page request can generate multiple DB lookups

for content, navigation, security, etc.

Page itself links and references images, CSS,

JavaScript, and other resources

SharePoint request lifecycle is complex

Better performance, better user experience

SharePoint caching: whatcha got?

Of interest to administrators (and what I will

be discussing) Object caching

BLOB caching

Page output caching

Office web applications cache

Of interest but not included Dev-related caching (Web Part cache, ASP.NET cache,

IVaryByCustomHandler implementation, post-cache

substitution, fragment caching, etc.)

Caching in SharePoint

Some plumbing information

Caching activation “Turned on” with (Office)

SharePoint Server

Publishing Infrastructure

Potentially bad news Not part of WSSv3 or

SharePoint Foundation

Some caching can be

used with non-publishing

sites, though

Some plumbing information

How it’s wired-in Supported through the

PublishingHttpModule

HttpModule wired into the

ASP.NET request pipeline

of all SharePoint web apps

Management Through web UI,

STSADM, PowerShell, and web.config changes

Consider a sample page …

Object caching

Speeds access to

frequently referenced

structural, property,

and result data Navigational data

Query results (cross-list

and cross-site)

Site properties

Page layouts

Object caching

Structure and operation A memory-backed cache on each WFE

Only cache that is “on” by default

Cache is assigned per site collection

100MB allocation per site collection by default

Conservative cache durations employed to avoid

displaying or using stale data

Additional control with SharePoint 2010 <ObjectCache> in web.config to govern maximum size

Object caching

Getting to it Via Site Collection

Administration section

on Site Settings page

Site Collection Object

Cache link

Object caching

Configuration

options Object Cache Size

Object Cache Reset

Cross List Query

Cache Changes

Cross List Query

Results Multiplier

Object caching

Recommendations Be careful with the Object Cache Size allocation!

Cross List Query Cache Changes

• Off by default for MOSS, on by default for SharePoint 2010

• Turn off or reduce time if queries are run against volatile data

• Turn on to reduce system loading and increase response time

Cross List Query Results Multiplier

• Increase if per-site and per-list permissions are in use,

especially if per-item permissions are also applied in lists

• Reduce for sites where anonymous access prevails

BLOB caching

Improves efficiency

and speed of serving

BLOB (Binary Large

OBject) data in lists Images and icons

Audio files

Video (including Flash)

Cascading style sheets

Javascript

BLOB caching

Structure and operation Also known as “disk-based caching”

Cache is backed by file system storage on WFEs

Turned “off” by default

Enabled and disabled per IIS web site

Disk allocation, file types cached, and client

cacheability settings are configurable

BLOB caching

Yields performance

improvements through (up to)

two different offloads Once enabled, reduces network traffic

between WFEs and content databases

Can also reduce load on WFEs by

instructing client browsers to cache

New in SharePoint 2010 HTTP byte range support, throttling

BLOB caching

Getting to it Accessed through the

web.config for each IIS site

What can be configured File system cache location

Pattern of files to be cached

Maximum disk space cache

can consume

Client cacheability (max-age)

Some service-related params

BLOB caching

<BlobCache> element in MOSS 2007

<BlobCache> element in SharePoint 2010

max-age attribute Easily added to yield client-side caching of BLOB assets

Client will use local assets without round-trips to server

BLOB caching

Recommendations Turn it on (that is, set enabled=“true”)

Adjust the location attribute to point to a data disk

Ensure enough disk space on WFEs to support sum of

maxSize attribute values (in GB) across web.config files

Do not attempt to manually manage BLOB cache contents.

• Do not delete individual cached files

• Use built-in flushes (2010) or CodePlex add-on (2007)

• If required, cache folder associated with IIS web site can be

deleted, but only when associated app pool is spun-down

If using the max-age attribute, understand the implications

Page output caching

Allows pages that

were rendered for

one user to be

stored and served to

other users

Piggybacks on

ASP.NET’s output

caching mechanism

Page output caching

Structure and operation Pages are rendered and stored in memory by key

• Key is composed of attributes specified by a caching profile

• Users with matching attributes can be served cached page

Cache is enabled per site collection

Page output cache is off by default

Primarily managed through a system of profiles

Additional control in SharePoint 2010 <OutputCacheProfiles> override in web.config file

Page output caching

Profiles specify caching characteristics User equivalence (cache key generation) criteria

How long pages are cached

Whether or not to check for updates on each request

How pages are cached on server and client

Custom caching parameters

Profiles can vary based on access type Authenticated profile assignment

Anonymous profile assignment

Page output caching

Step 1 Review the cache

profiles that are defined

• Via Site Collection

Administration section

on Site Settings menu

• Site Collection Cache

Profiles link

Create your own

profiles if desired

Page output caching

Step 2 Apply caching profiles

for site collection

• Via Site Collection

Administration section

on Site Settings menu

• Site Collection Output

Cache link

Indicate if profiles can

vary by sub-site and

layout page type

Page output caching

Step 3 Optionally apply

different profiles to sub-

sites as needed

• Via each Site

Administration section on

Site Settings menu

• Site Output Cache link

Inheritance model used

Can push down the

hierarchy with checkbox

Page output caching

Step 4 Optionally apply

different profiles per

page layout type

• Via Galleries section on

Site Settings menu

• Master Pages And Page

Layouts link

• Edit properties of target

page layout

• Save and check-in

Page output caching

Step 5 Enable output cache

• Via Site Collection

Administration section

on Site Settings menu

• Site Collection Output

Cache link

Optional debug info

can be written as

HTML comments to

bottom of each page

Page output caching

Recommendations Biggest bang comes in purely anonymous usage scenarios

• Caching becomes less attractive as user equivalence drops

Perform extensive multi-user concurrent testing before

implementing in production

• Test each profile scenario in-use (authenticated/anonymous)

• Test deviation scenarios (per-site/per-layout profile use)

• Failure to tune properly can result in information “leaking” from

one user to another

Debug cache information is your friend

• Helps you understand how page was evaluated and rendered

Office Web Apps Cache

Specific to SharePoint 2010

Office Web Apps Cache

What it is A standard SharePoint site collection (Team Site)

• Relative URL: /sites/Office_Viewing_Service_Cache

Office Web Apps Cache Creation timer job creates it

Houses rendered images and XAML for Office docs

One created per web application

Defaults Allowed to grow to 100GB

Documents live for 30 days until they are removed by the

Office Web Apps Expiration timer job

Office Web Apps Cache

Recommendations Relocate cache to a dedicated database using

Set-OfficeSPWebAppsCache PowerShell cmdlet

• Once in its own DB, it can be excluded from backups

For web apps housing largely static Office docs

• Increase cache expiration period

• Increase cache size

For web apps where Office content is volatile

• Decrease cache expiration period

• Decrease cache size

Warnings and Watch-outs

Object caching

ACTION Cache size reduced (significantly) below 100MB

POTENTIAL RESULT Object cache fills and becomes memory constrained

Resource contention and ejections lead to cache compactions

Under heavy load, nature of compaction process leads to thrashing

SharePoint’s ability to serve pages falls through the floor

WHAT TO WATCH Total Number Of Cache Compactions perf counter

Publishing Cache Hit Ratio perf counter

Page output caching

OBSERVATION User A requests a page. User B requests same page.

User B sees information tied to User A

POTENTIAL CAUSE Page output cache profile isn’t granular enough

WHAT YOU CAN DO Refine the output profile in-use (use additional attributes)

Set caching exclusions by sub-site or page layout type

Use post-cache substitution (donut caching) in custom code

Leverage custom caching handler (IVaryByCustomHandler)

Page output caching

OBSERVATION Memory consumption of ASP.NET worker process

grows significantly; performance may deteriorate

POTENTIAL CAUSE Too many pages being cached (excessive memory load)

WHAT YOU CAN DO Adjust caching profiles if possible to reduce page load

Selectively disable caching for highly varying sub-sites

Adjust cache element values in web.config that control

ASP.NET worker process (e.g.,privateBytesLimit)

BLOB caching

OBSERVATION Path property is set correctly, but images stored in site

collection aren’t being cached in file system

POTENTIAL CAUSE BLOB cache only works with resources that are stored within

list items in lists or document libraries

WHAT YOU CAN DO Leverage built-in libraries such as Site Collection Images

Move resources to a custom list

BLOB caching

OBSERVATION Image is changed on a SharePoint site. Some client

browsers show new image, others show old image.

POTENTIAL CAUSE max-age attribute is in-use with BLOB caching

WHAT YOU CAN DO Instruct clients to clear their browser cache

Avoid using the max-age attribute with web apps serving

site collections housing very volatile BLOB content

This behavior is by design

Questions?

References and Resources

“Caching in Office SharePoint Server 2007” http://technet.microsoft.com/en-us/library/cc298466(office.12).aspx

“Configure cache settings for a Web application

(SharePoint Server 2010)” http://technet.microsoft.com/en-us/library/cc770229.aspx

“Disk-Based Caching for Binary Large Objects” http://msdn.microsoft.com/en-us/library/aa604896.aspx

“Manually Clearing the MOSS 2007 BLOB Cache” http://sharepointinterface.com/2009/10/30/manually-clearing-the-moss-

2007-blob-cache/

References and Resources

MOSS 2007 Farm-Wide BLOB Cache Flushing Solution http://blobcachefarmflush.codeplex.com/

“Manage the Office Web Apps cache” http://technet.microsoft.com/en-us/library/ee837422.aspx

“MOSS Object Cache Memory Tuning is not an Intuitive

Process” http://sharepointinterface.com/2009/08/30/moss-object-cache-memory-

tuning-is-not-an-intuitive-process/

“cache Element for caching (ASP.NET Settings Schema)” http://msdn.microsoft.com/en-us/library/ms228248.aspx

Contact information

Sean McDonough Blog: http://SharePointInterface.com

Email: sean@SharePointInterface.com

LinkedIn: http://www.linkedin.com/in/smcdonough

Twitter: @spmcdonough

The SharePoint 2007 Disaster Recovery Guide

http://tinyurl.com/SPDRBook

The SharePoint 2010 Disaster Recovery Guide http://tinyurl.com/SPDRBook2010